This invention relates to a thermoplastic resin composition which is a blend of a thermoplastic urethane elastomer and a specifically selected thermoplastic fluororesin having flexibility. The resin composition is particularly suitable for extrusion to form, for example, tubes or coverings of electric wires or cables.
Urethane elastomers are widely used as thermoplastic resins having excellent mechanical properties. In particular urethane elastomers having a glass transition temperature lower than room temperature are largely used as extrusion molding materials to form various tubes and coverings of electric wires and cables.
However, from some aspects thermoplastic urethane elastomers have disadvantages too. First, compared with more popular thermoplastic resins such as polyvinyl chloride resins conventional urethane elastomers are generally inferior in extrudability and hence offer greater load to extruders. Therefore, when an urethane elastomer is extruded with an extruder primarily designed for extrusion of other thermoplastic resins it is likely that the extrusion output per unit time and some other items of extrusion conditions are unstable by reason of insufficient power of the extruder.
Thermoplastic urethane elastomers relatively low in hardness have another disadvantage that the extrusion molded products have considerably tacky surfaces. When the products such as tubes or covered wires are left stacked at room temperature the products stick to each other, and in some cases the struck products cannot easily be separated from one another. In industrial practice it is often to apply an antisticking agent in the form of powder or paste to the extruded products of urethane elastomer, but the application of such a powder or paste is troublesome and in many cases raises the need of removing the antisticking agent at the stage of using the extruded products. In some cases the tacky products tend to stick to articles made of different materials and consequently raise certain problems. For example, when a cable having an urethane elastomer covering is used in an industrial robot there is a possibility that the cable sticks to a rack or another cable covered with a different material and consequently breaks as the robot repeats preprogrammed operations.
Besides, as covering materials for electric wires and cables conventional thermoplastic urethane elastomers are not fully satisfactory in resistance to heat aging and in this respect are inferior to conventional fluororesins.